Structure of C3v phosphoranyl and C4v phosphorane anion radicals. A quantum-chemical study

Ab initio molecular orbital calculations on various C,, phosphoranyl radicals and the C,, PF5-phosphorane anion radical are presented.By the unrestricted Hartree-Fock method with a 4-31G basis set the geometries for C,, XaPXe3 (Xa = apical ligand, Xe = equatorial ligand) radicals were optimized for X = H, F , and C1.All C,, radicals reveal a trigonal-bipyrimidal structure with the unpaired electron in apical position.The optimized PF,-radical is octahedral with the unpaired electron acting as a ligand.The calculated isotropic hyperfine coupling constants are in good agreement with the experimental values.Variation of the apical-equatorial bond angle for HPH3 and PF5-leads to u*-arrangements.A detailed study of the C,, PH, + Ha potential energy surface is described.It appears that a u*-arrangement is not stable but leads to dissociation.The stability of XaPH3 with respect to dissociation into PH3 and Xa. is described, and transition states are calculated.HPH3 lies 43.2 kJ mol-I below its transition state, FPH, (9.8 kJ mol-'), whereas CIPH, is unstable.